Counter anecdote time.
I was playing in a D&D campaign about the same time, and the DM was using Keep on the Borderlands as a base. No problems. The DM was very adamant that this was a sandbox type campaign with the players having a lot of freedom. The group decided to rob the jewel merchant in the Keep. We spent most of an entire session planning the heist, doing tons of RP in character, learning the layout of things, getting schedules all that sort of thing. We wrap up the session with the plan in place and we would play it out the next session. All week the players are talking about this. The entire group is really excited.
Next week starts and the jewel merchant has closed up shop and left in the middle of the night. No warning, no note, absolutely no trail left behind. Can't follow him, he's got too much of a lead.
Now, I've told this story before on these boards and had multiple people say that the DM is not, in any way, railroading here. This was just the "objective" results of the campaign. The group quit on the spot. We all, as a group, thanked the DM politely and walked. The DM continued to have quite successful games with other groups that swore up and down that she wasn't railroading.
So, no, I really don't think terrible DM's are all dysfunctional, socially inept individuals. And, again, this is why I talk about, from the player's perspective, good and bad DM's look and do exactly the same thing and it's often impossible to tell the difference.